Single-layer complete heat-insulation systems for the exterior insulation of the walls of buildings are known. They consist of insulating boards of rigid expanded plastic, polystyrene in particular, cemented to the outer surface of the building with a mortar preparation or composition and provided with a coating of dispersion plaster. The material-specific shrinkage of expanded-plastic boards and the effects of temperature and weather result in considerable stress in the exterior insulation-composition system, especially between the boards and the plaster coating, which can lead to the plaster shearing off and to cracks in the coating, especially where the boards abut one another, even though a woven reinforcement is usually embedded in the outer plaster to prevent cracking. Providing at least the outside of the plastic boards with assemblages of longitudinal and transverse incisions deeper than half the thickness of the board is known (EPA No. 0 015 564) is known. This is intended to prevent stress peaks at the joints between the boards and to extensively eliminate cracks in the coating. To improve the adhesion of the mortar preparation and especially of the undercoat to the board, one or both surfaces are provided with dove-tailed grooves. Although the boards usually have a rectangular cross-section with the abutting edges perpendicular to the surface, surrounding them with an interlocking rabbet is also known (German AS No. 1 658 875).
Since the known anti-cracking measures, which relate to the plastic itself and to its preliminary treatment--to adequate aging and to preparation of the outside and inside surfaces and on occasion of the abutting edges for example--are not absolutely reliable, it is still necessary to reinforce the plaster or other coating with a woven fabric.